Average Peak Amplitude Research Articles

The role of altered tissue osmolality on the characteristics and propagation of seizure activity in the intact isolated mouse hippocampus

To study the role of altered tissue osmolality on the characteristics and propagation dynamics of seizure activity and on interictal activity, in a low-Mg(+2) artificial cerebrospinal fluid (ACSF) model of recurrent seizures, using the immature (P8-P25) intact isolated mouse hippocampus. Recordings were obtained extracellularly from a single site in the CA1 region and from multiple sites along the septotemporal axis measuring spontaneous epileptiform field activity in ACSFs of different osmolalities. In normal osmolar ACSF (310 mOsmol), the average duration of recorded seizures was 90+/-10 s and the average peak amplitude was 0.9+/-0.1 mV. In a hypoosmolar ACSF (270 mOsmol), the seizures were significantly prolonged at 165+/-20 s (p<0.05) with a peak amplitude of 1.2+/-0.3 mV, whereas interictal activity was suppressed. Hyperosmolar ACSF (340 mOsmol) reduced the duration (65+/-15 s) and peak amplitude (0.6+/-0.1 mV, p<0.05) from control, but interictal activity was not affected. No differences in seizure recurrence rate were noted in all three osmolar states. The present study, the first to assess of the role of altered tissue osmolality in an intact in vitro preparation, demonstrates that changes in perfusate osmolality play a significant role on the amplitude, duration, and propagation velocity of seizure-like events, and the characteristics of interictal activity, without affecting seizure recurrence rate. Increasing tissue osmolality should be considered as a valid target for anticonvulsant treatment.

A Conserved Cys-loop Receptor Aspartate Residue in the M3-M4 Cytoplasmic Loop Is Required for GABAA Receptor Assembly

Members of the Cys-loop superfamily of ligand-gated ion channels, which mediate fast synaptic transmission in the nervous system, are assembled as heteropentamers from a large repertoire of neuronal subunits. Although several motifs in subunit N-terminal domains are known to be important for subunit assembly, increasing evidence points toward a role for C-terminal domains. Using a combination of flow cytometry, patch clamp recording, endoglycosidase H digestion, brefeldin A treatment, and analytic centrifugation, we identified a highly conserved aspartate residue at the boundary of the M3-M4 loop and the M4 domain that was required for binary and ternary gamma-aminobutyric acid type A receptor surface expression. Mutation of this residue caused mutant and partnering subunits to be retained in the endoplasmic reticulum, reflecting impaired forward trafficking. Interestingly although mutant and partnering wild type subunits could be coimmunoprecipitated, analytic centrifugation studies demonstrated decreased formation of pentameric receptors, suggesting that this residue played an important role in later steps of subunit oligomerization. We thus conclude that C-terminal motifs are also important determinants of Cys-loop receptor assembly.

Cadmium Reduces Contractile Responses of Rat Duodenum, In Vitro

The present study focuses on the effects of cadmium in drinking water on rat duodenum contractility, in vitro. Two experimental groups (n = 10 each) were administered with 15 ppm cadmium chloride in their drinking water for 1 and 2 months, respectively. Two separate groups (n = 10 each) were maintained in similar conditions but received no cadmium and acted as controls. After the experimental period, the duodenal segment responses were measured by means of an isotonic transducer. The average peak amplitude of acetylcholine-induced contractions was significantly decreased in both cadmium-treated groups. Incubation of duodena from the cadmium-free controls with atropine or in a calcium-free medium resulted in reduced contractility that was undistinguishable from that of the cadmium-treated rats. Cadmium reduces the contractile response apparently by directly or indirectly decreasing cellular calcium influx.

Lamotrigine inhibits postsynaptic AMPA receptor and glutamate release in the dentate gyrus

The dentate gyrus (DG) is a gateway that regulates seizure activity in the hippocampus. We investigated the site of action of lamotrigine (LTG), an effective anticonvulsant, in the regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-D-aspartic acid (NMDA) receptor-mediated excitatory synaptic transmission on DG. Evoked AMPA and NMDA receptor-mediated excitatory postsynaptic currents (eEPSCampa and eEPSCnmda) were recorded by whole-cell patch-clamp recording from the granule cells of DG in brain slice preparation of young Wistar rats (60-120 g). Exogenously applied AMPA and NMDA-induced currents and AMPA receptor-mediated miniature EPSC (mEPSCampa) were recorded in the presence of specific antagonists. LTG inhibited both eEPSCampa and eEPSCnmda, and had no effect on exogenously applied NMDA-induced current indicating LTG inhibited glutamate release. Previous studies demonstrated that alteration in glutamate concentration in synaptic cleft causes parallel changes of eEPSCampa and eEPSCnmda. Our results showed that LTG inhibited eEPSCampa significantly more than eEPSCnmda (p < 0.05), suggesting that LTG may also have blocked the postsynaptic AMPA receptor. The hypothesis is further supported by the facts that; (1) LTG (30-100 microM) inhibited direct exogenously applied AMPA-induced currents (to 90%), (2) LTG significantly reduced the amplitude, but not the frequency of mEPSCampa and asynchronous (EPSC), and (3) LTG-induced reduction of eEPSCampa was not associated with a modification of the paired-pulse ratio. To sum up, LTG exerts a postsynaptic inhibitory mechanism on the AMPA receptor. Our results demonstrate that LTG suppresses postsynaptic AMPA receptors and reduces glutamate release in granule cells of DG. The postsynaptic effect can be one of the underlying mechanisms of LTG's anticonvulsant action.

TARP Subtypes Differentially and Dose-Dependently Control Synaptic AMPA Receptor Gating

A family of transmembrane AMPA receptor regulatory proteins (TARPs) profoundly affects the trafficking and gating of AMPA receptors (AMPARs). Although TARP subtypes are differentially expressed throughout the CNS, it is unclear whether this imparts functional diversity to AMPARs in distinct neuronal populations. Here, we examine the effects of each TARP subtype on the kinetics of AMPAR gating in heterologous cells and in neurons. We report a striking heterogeneity in the effects of TARP subtypes on AMPAR deactivation and desensitization, which we demonstrate controls the time course of synaptic transmission. In addition, we find that some TARP subtypes dramatically slow AMPAR activation kinetics. Synaptic AMPAR kinetics also depend on TARP expression level, suggesting a variable TARP/AMPAR stoichiometry. Analysis of quantal synaptic transmission in a TARP gamma-4 knockout (KO) mouse corroborates our expression data and demonstrates that TARP subtype-specific gating of AMPARs contributes to the kinetics of native AMPARs at central synapses.

Length‐Dependence of Lymphatic Phasic Contractile Activity Under Isometric and Isobaric Conditions

Experiments were designed to determine if the effect of preload on the spontaneous contractile activity of rat mesenteric lymphatics would be different under isometric and isobaric conditions. Isobaric protocols on cannulated, pressurized rat mesenteric lymphatics ( approximately 120 microm, ID) measured the effects of lumenal pressure on contraction amplitude, frequency, and rate of diameter change (dD/dt). Analogous protocols were conducted using a wire myograph to determine the effects of passive force (preload) on the characteristics of spontaneous, isometric force transients. Servo-control systems allowed responses to ramp or step increases in preload/pressure to be tested. Under isobaric conditions, contraction amplitude was maximal at the lowest pressure tested (1 cm H(2)O), and progressively declined with pressure elevation to 10 cm H(2)O. Changes in dD/dt followed a similar pattern. In contrast, contraction frequency progressively increased with pressure. Under isometric conditions, the amplitude of spontaneous force transients was maximal at preloads of 0.3-0.4 mN, with dF/dt following a similar pattern; the average peak amplitude was approximately 15% of the maximal active contractile force developed during agonist stimulation. The frequency of the transients increased with preload from 0.05 to 0.3 mN, and remained constant at higher preloads. The amplitude-frequency product, an estimate of lymphatic pumping ability, reached a maximum value at 0.4 mN in isometric vessels and at 6 cm H(2)O in isobaric vessels. Isometric and isobaric methods yielded qualitatively similar indices of spontaneous contractile activity. However, the ranges of amplitude and frequency changes were much greater under isobaric conditions (3- to 5-fold) than under isometric conditions (50-80%).

α2A-Adrenoceptors Strengthen Working Memory Networks by Inhibiting cAMP-HCN Channel Signaling in Prefrontal Cortex

Spatial working memory (WM; i.e., "scratchpad" memory) is constantly updated to guide behavior based on representational knowledge of spatial position. It is maintained by spatially tuned, recurrent excitation within networks of prefrontal cortical (PFC) neurons, evident during delay periods in WM tasks. Stimulation of postsynaptic alpha2A adrenoceptors (alpha2A-ARs) is critical for WM. We report that alpha2A-AR stimulation strengthens WM through inhibition of cAMP, closing Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels and strengthening the functional connectivity of PFC networks. Ultrastructurally, HCN channels and alpha2A-ARs were colocalized in dendritic spines in PFC. In electrophysiological studies, either alpha2A-AR stimulation, cAMP inhibition or HCN channel blockade enhanced spatially tuned delay-related firing of PFC neurons. Conversely, delay-related network firing collapsed under conditions of excessive cAMP. In behavioral studies, either blockade or knockdown of HCN1 channels in PFC improved WM performance. These data reveal a powerful mechanism for rapidly altering the strength of WM networks in PFC.

Short-Term Hormone Release from Adult Female Rat Hypothalamic and Pituitary Explants is not Altered by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

2, 3, 7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has adverse effects on reproduction, in part due to direct actions at the ovary. It is unclear whether effects are further mediated by glands that regulate ovarian function. We investigated whether effects of TCDD are mediated via the hypothalamic-pituitary axis. Hypothalamic and pituitary tissues were cultured in medium with and without TCDD. TCDD did not alter GnRH release from hypothalamic samples. It continued to be pulsatile with no differences in the average peak frequency, average peak amplitude, or baseline GnRH release. TCDD did not alter GnRH-induced release of gonadotropins from pituitary samples. There were no differences in average peak amplitude or baseline release. AhR, ARNT or ER alpha mRNA copy numbers in cultured pituitaries were not affected by TCDD. Our data suggest that TCDD effects on ovarian function are not mediated through the hypothalamic or pituitary release parameters tested in this study.

Anti‐homeostatic synaptic plasticity of glycine receptor function after chronic strychnine in developing cultured mouse spinal neurons

In this study, we describe a novel form of anti-homeostatic plasticity produced after culturing spinal neurons with strychnine, but not bicuculline or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Strychnine caused a large increase in network excitability, detected as spontaneous synaptic currents and calcium transients. The calcium transients were associated with action potential firing and activation of gamma-aminobutyric acid (GABA(A)) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors as they were blocked by tetrodotoxin (TTX), bicuculline, and CNQX. After chronic blockade of glycine receptors (GlyRs), the frequency of synaptic transmission showed a significant enhancement demonstrating the phenomenon of anti-homeostatic plasticity. Spontaneous inhibitory glycinergic currents in treated cells showed a fourfold increase in frequency (from 0.55 to 2.4 Hz) and a 184% increase in average peak amplitude compared with control. Furthermore, the augmentation in excitability accelerated the decay time constant of miniature inhibitory post-synaptic currents. Strychnine caused an increase in GlyR current density, without changes in the apparent affinity. These findings support the idea of a post-synaptic action that partly explains the increase in synaptic transmission. This phenomenon of synaptic plasticity was blocked by TTX, an antibody against brain-derived neurotrophic factor (BDNF) and K252a suggesting the involvement of the neuronal activity-dependent BDNF-TrkB signaling pathway. These results show that the properties of GlyRs are regulated by the degree of neuronal activity in the developing network.

Predicting Models of Coal Thickness Based on Seismic Attributions and Their Applications

AbstractAs a technology widely used in lithology and structure interpretation, seismic attribute technology has been playing an important role in coal and oil exploration. Based on 3‐D seismic exploration data of coal seam 13‐1 in the Xieqiao colliery, Huainan coal field of China, 28 seismic attributes are extracted. Through analysis of seismic attributes, four usable seismic attributes, including average peak amplitude, kurtosis in amplitude, maximum absolute amplitude and slope rate of instantaneous frequency, are selected as the basic parameters of predicting models of coal thickness. Combined with the real drill data, the predicting models between coal thickness and multi attributes are established by using analytical methods of multivariant polynomial regression and BP neural networks (BPNN), and error analysis of predicting coal thickness is carried out. From the comparison of predicting results of coal thickness of coal seam 13‐1 in the Xieqiao colliery, Huainan coal field of China by using these two models, it is shown that BPNN model has higher accuracy in predicting coal thickness.

Does antinerve growth factor affect isolated ileal contractility in rat?

This study investigates the effects of antinerve growth factor (anti-NGF) application on isolated ileal contractility in the rat. For this purpose, rats were divided into four groups. The control animals (n=8) received only intraperitoneal injection of an isotonic NaCl solution (i.p). Anti-NGF was daily administered intraperitoneally at the dose of 1 ng/g level in the first experimental group (n=8), and at doses of 10 ng/g (n=7) and 40 ng/g (n=7) in the second and third experimental groups, respectively. Seven days after the injections rats were sacrificed and ileum segments were isolated. Responses to acetylcholine (ACh) were evaluated by using standard Tyrode, double-calcium Tyrode and calcium-free Tyrode solutions. The average peak amplitude of ACh-induced contractions recorded in standard Tyrode solution was significantly decreased in all three experimental groups as compared to the control group (p 0.05). When double-calcium Tyrode solution was used as the perfusion medium, the responses to ACh were also lower in all anti-NGF applied groups as compared to its control group (p 0.05). Our results showed that the application of anti-NGF reduced the contractile responses of the rat isolated ileum apparently by decreasing the calcium influx from the extracellular medium.

Activation of a calcium-activated cation current during epileptiform discharges and its possible role in sustaining seizure-like events in neocortical slices.

Epileptic seizures are composed of recurrent bursts of intense firing separated by periods of electrical quiescence. The mechanisms responsible for sustaining seizures and generating recurrent bursts are yet unclear. Using whole cell voltage recordings combined with intracellular calcium fluorescence imaging from bicuculline (BCC)-treated neocortical brain slices, I showed isolated paroxysmal depolarization shift (PDS) discharges were followed by a sustained afterdepolarization waveform (SADW) with an average peak amplitude of 3.3 +/- 0.9 mV and average half-width of 6.2 +/- 0.6 s. The SADW was mediated by the calcium-activated nonspecific cation current (I(can)) as it had a reversal potential of -33.1 +/- 6.8 mV, was unaffected by changing the intracellular chloride concentrations, was markedly diminished by buffering [Ca(2+)](i) with intracellular bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA), and was reversibly abolished by the I(can) blocker flufenamic acid (FFA). The Ca(2+) influx responsible for activation of I(can) was mediated by both N-methyl-d-aspartate-receptor channels, voltage-gated calcium channels and, to a lesser extent, internal calcium stores. In addition to isolated PDS discharges, BCC-treated brain slices also produced seizure-like events, which were accompanied by a prolonged depolarizing waveform underlying individual ictal bursts. The similarities between the initial part of this waveform and the SADW and the fact it was markedly reduced by buffering [Ca(2+)](i) with BAPTA strongly suggested it was mediated, at least in part, by I(can). Addition of FFA reversibly eliminated recurrent bursting, and transformed seizure-like events into isolated PDS responses. These results indicated I(can) was activated during epileptiform discharges and probably participated in sustaining seizure-like events.

Acid-sensing Ion Channel 2 (ASIC2) Modulates ASIC1 H+-activated Currents in Hippocampal Neurons

Hippocampal neurons express subunits of the acid-sensing ion channel (ASIC1 and ASIC2) and exhibit large cation currents that are transiently activated by acidic extracellular solutions. Earlier work indicated that ASIC1 contributed to the current in these neurons and suggested its importance for normal behavior. However, the specific contribution of ASIC1 and ASIC2 subunits to acid-evoked currents in hippocampal neurons remained uncertain. To decipher the individual role of the ASIC subunits, we studied H(+)-gated currents in neurons from both ASIC1 and ASIC2 null mice. We found that much of the current was produced by ASIC1a/2a heteromultimeric channels, and individual subunits made distinct contributions. The ASIC1a subunit was key in establishing current amplitude. The ASIC2a subunit had little effect on amplitude but influenced desensitization, recovery from desensitization, pH sensitivity, and the response to modulatory agents. We also found heterogeneity in the contribution of ASIC2 throughout the neuronal population, with individual neurons expressing both ASIC1a homomultimeric and ASIC1a/2a heteromultimeric channels. Studies of neurons heterozygous for disrupted ASIC alleles indicated that the properties of H(+)-gated currents are dependent on the proportion of the individual subunits. These findings indicate that the absolute and relative amounts of ASIC subunits determine the amplitude and properties of hippocampal H(+)-gated currents and therefore may contribute to normal physiology and pathophysiology.

Activation of NMDA receptors in rat dentate gyrus granule cells by spontaneous and evoked transmitter release.

Activation of N-methyl-D-aspartate (NMDA) receptors by synaptically released glutamate in the nervous system is usually studied using evoked events mediated by a complex mixture of AMPA, kainate, and NMDA receptors. Here we have characterized pharmacologically isolated spontaneous NMDA receptor-mediated synaptic events and compared them to stimulus evoked excitatory postsynaptic currents (EPSCs) in the same cell to distinguish between various modes of activation of NMDA receptors. Spontaneous NMDA receptor-mediated EPSCs recorded at 34 degrees C in dentate gyrus granule cells (DGGC) have a frequency of 2.5 +/- 0.3 Hz and an average peak amplitude of 13.2 +/- 0.8 pA, a 10-90% rise time of 5.4 +/- 0.3 ms, and a decay time constant of 42.1 +/- 2.1 ms. The single-channel conductance estimated by nonstationary fluctuation analysis was 60 +/- 5 pS. The amplitudes (46.5 +/- 6.4 pA) and 10-90% rise times (18 +/- 2.3 ms) of EPSCs evoked from the entorhinal cortex/subiculum border are significantly larger than the same parameters for spontaneous events (paired t-test, P < 0.05, n = 17). Perfusion of 50 microM D(-)-2-amino-5-phosphonopentanoic acid blocked all spontaneous activity and caused a significant baseline current shift of 18.8 +/- 3.0 pA, thus identifying a tonic conductance mediated by NMDA receptors. The NR2B antagonist ifenprodil (10 microM) significantly reduced the frequency of spontaneous events but had no effect on their kinetics or on the baseline current or variance. At the same time, the peak current and charge of stimulus-evoked events were significantly diminished by ifenprodil. Thus spontaneous NMDA receptor-mediated events in DGGC are predominantly mediated by NR2A or possibly NR2A/NR2B receptors while the activation of NR2B receptors reduces the excitability of entorhinal afferents either directly or through an effect on the entorhinal cells.

Glycine receptors and glycinergic synaptic transmission in the deep cerebellar nuclei of the rat: a patch-clamp study.

To clarify possible glycinergic transmission in the cerebellum, principal neurons in deep cerebellar nuclei (DCN) of sliced cerebella (200 microm in thickness) from rats (aged 2-14 days) were studied using whole cell patch-clamp techniques. When glycine (100 microM) was applied to the DCN neurons from a "Y tube," large outward currents were induced (average peak amplitude of about 600 pA at -40 mV). The currents were blocked by strychnine (1 microM) and showed a reversal potential of -62 mV, which was approximately the estimated Cl- equilibrium potential. The dose-response relation of the currents showed an apparent dissociation constant of 170 microM for glycine and Hill coefficient of 1.6. In the presence of 6-cyano-7-nitroquinoziline-2, 3-dione (CNQX), d-(-)-2-amino-5-phosphonovaleric acid (APV) and bicuculline, which antagonize amino-3-hydroxy-5-methyl-isoxazol-propionate (APMA), N-methyl-d-aspartate (NMDA), and GABAA receptors, respectively, postsynaptic currents sensitive to strychnine (1 microM) were induced in DCN neurons by external perfusion of 20 mM K+ saline. Electrical stimulation of surrounding tissues in DCN evoked definite inhibitory postsynaptic currents (IPSCs) in these neurons. The IPSCs had a reversal potential of -62 mV and showed sensitivities to strychnine and tetrodotoxin. Thus this study has revealed that strychnine-sensitive glycine receptors are expressed in neurons of the DCN of rats and that glycinergic transmission mediated by these receptors is functional in these neurons from stages immediately after birth. The glycinergic innervations are presumably supplied by small interneurons located in the DCN.

Functional properties of spontaneous EPSCs and non-NMDA receptors in rod amacrine (AII) cells in the rat retina.

The functional properties of spontaneous, glutamatergic EPSCs and non-NMDA receptors in AII amacrine cells were studied in whole cells and patches from slices of the rat retina using single and dual electrode voltage clamp recording. Pharmacological analysis verified that the EPSCs (Erev approximately 0 mV) were mediated exclusively by AMPA-type receptors. EPSCs displayed a wide range of waveforms, ranging from simple monophasic events to more complex multiphasic events. Amplitude distributions of EPSCs were moderately skewed towards larger amplitudes (modal peak 23 pA). Interevent interval histograms were best fitted with a double exponential function. Monophasic, monotonically rising EPSCs displayed very fast kinetics with an average 10-90 % rise time of approximately 340 micro s and a decay phase well fitted by a single exponential (taudecay approximately 760 micro s). The specific AMPA receptor modulator cyclothiazide markedly slowed the decay phase of spontaneous EPSCs (taudecay approximately 3 ms). An increase in temperature decreased both 10-90 % rise time and taudecay with Q10 values of 1.3 and 1.5, respectively. The decay kinetics were slower at positive membrane potentials compared to negative membrane potentials (205 mV/e-fold change in taudecay). Step depolarization of individual presynaptic rod bipolar cells or OFF-cone bipolar cells evoked transient, CNQX-sensitive responses in AII amacrine cells with average peak amplitudes of approximately 330 pA. Ultrafast application of brief (approximately 1 ms) or long (approximately 500 ms) pulses of glutamate to outside-out patches evoked strongly desensitizing responses with very fast deactivation and desensitization kinetics, well fitted by single (taudecay approximately 1.1 ms) and double exponential (tau1 approximately 3.5 ms; tau2 approximately 21 ms) functions, respectively. Double-pulse experiments indicated fast recovery from desensitization (tau approximately 12.4 ms). Our results indicate that spontaneous, AMPA receptor-mediated EPSCs in AII amacrine cells have very fast, voltage-dependent kinetics that can be well accounted for by the kinetic properties of the AMPA receptors themselves

Average characteristics and activity dependence of the subauroral polarization stream

Data from the Millstone Hill incoherent scatter radar taken over two solar cycles (1979–2000) are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere. Radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes, and these scans have been examined for all local times and activity conditions.We examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two‐cell convection. Individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream (SAPS), which spans the nightside from dusk to the early morning sector for all Kp greater than 4. Premidnight, the SAPS westward convection lies equatorward of L = 4 (60° invariant latitude, Λ), spans 3°–5° of latitude, and has an average peak amplitude of &gt;900 m/s. In the predawn sector, SAPS is seen as a region of antisunward convection equatorward of L = 3 (55° Λ), spanning ∼3° of latitude, with an average peak amplitude of 400 m/s.

Spontaneous activity-independent intracellular calcium signals in the developing spinal cord of the zebrafish embryo

Calcium signals play an important role in a variety of processes necessary for neuronal development. Whilst the characteristics and function of calcium signals have been comprehensively examined in vitro, the significance of these signals during development in an intact embryo remains unclear. In this study, we have examined the spatial and temporal patterns of intracellular calcium signals in precursor cells (cells without processes) within the spinal cord of the intact zebrafish embryo aged between 17 and 27 h. In total, approximately one-third of cells displayed spontaneous intracellular calcium transients. The calcium transients had an average peak amplitude of 33.3 (±2.8%) above baseline, a duration of 52.2 (±6.3 s) and occurred with an average frequency of 4.6 (±0.4 per hour). Calcium transients were observed in precursor cells located throughout the spinal cord, with the highest percentage of active cells (35.1±8%) occurring at a developmental time of 21–22 h. Furthermore these intracellular calcium signals were observed in the presence of tricaine, indicating that they are not generated via sodium-dependent action potentials. In precursor cells loaded with the calcium buffer BAPTA both the frequency and the amplitude of the calcium transients was significantly reduced. The intracellular calcium transients may represent a common activity-independent calcium-mediated mechanism that contributes to the regulation of neuronal development in the spinal cord of the zebrafish embryo during the segmentation and early pharyngula period.

Non-linear, high-gain and sustained-to-transient signal transmission from rods to amacrine cells in dark-adapted retina of Ambystoma.

In darkness, On-Off amacrine cells (ACs) of the tiger salamander retina exhibited large spontaneous transient depolarizing potentials (sTDPs) with average peak amplitude of 5.05 +/- 2.5 mV and average frequency of 0.42 +/- 0.25 s(-1). Under voltage-clamp conditions the cell displayed large spontaneous postsynaptic currents (sPSCs) with average peak amplitude of 98 +/- 39 pA and average frequency of 0.45 +/- 0.22 s(-1). To a light step, ACs gave rise to a transient 'On' response at the light onset and a transient 'Off' response at light offset, followed by a train of TDPs ('After' response). Near the response threshold (0.3 activated rhodopsin molecules per rod per second), light-evoked TDPs (leTDPs) of similar amplitude and kinetics as the large sTDPs observed in darkness were seen, and about half of these leTDPs elicited a regenerative potential (RP). Brighter light steps gave rise to more leTDPs and higher rates of RPs in the On, Off and After responses. Within the linear response range of the rods, the AC response was non-linear, with the highest gain (676 +/- 429) near the dark potential. The amplitude of Off responses increased with the duration of the light step, and ACs may use this to encode speeds of moving stimuli: the faster the light object moves, the smaller the AC Off response. Moreover, the number of leTDPs in the AC After response increased with light intensity, and the onset of the After response coincides with bipolar cell tail response recovery. One possible origin of the large sTDPs and leTDPs is the spontaneous and depolarization-induced regenerative calcium potentials (RCaPs) in bipolar cell synaptic terminals. RCaPs in bipolar cell synaptic terminals cause transient glutamate release that results in the sTDPs in darkness, and leTDPs in On, Off and After responses in ACs.

Optical recording of spreading depression in rat neocortical slices

A spreading depression (SD) was elicited in adult rat neocortical slices by microdrop application of high potassium and the SD propagation pattern was analyzed by recording simultaneously the extracellular DC potential and the changes in the intrinsic optical signal. The electrical SD with an average peak amplitude of 13.2±3.4 mV showed a good spatial and temporal correlation with the optical signal. In 79% of the slices, the SD was characterized by an initial increase of light reflectance by 2.3±1.6%, followed by a reflectance decrease of 0.5±2.4% and finally a larger and long-lasting increase by 5±2.4%. In the remaining slices, the SD revealed an initial decrease in light reflectance by 5.8±1.8% followed by an increase of 1.4±1.2%. In all slices, the recovery in the DC recording was faster as in the optical signal. The SD preferentially propagated within layers I–IV and could be blocked in most experiments by a vertical incision through upper layers or by local glutamate receptor blockade following microdrop application of kynurenic acid in layers II–III. The SD could be also blocked by bath application of kynurenic acid, MK-801 and octanol, but not by the more specific gap junction blocker carbenoxolone. Our results indicate that the high density of dendritic processes and glutamate receptors in layers II–IV promote the horizontal spread of the SD in these cortical layers and that gap junctions are not required for the propagation of SD in neocortical slices.